The invention relates generally to semiconductor devices and integrated circuit fabrication and, in particular, to circuits for programming an electrical fuse, methods for programming an electrical fuse, and methods for designing a silicon-controlled rectifier used to program an electrical fuse.
Programmable devices, such as electrical fuses (i.e., efuses), are used in various programmable integrated circuits, such as redundancy circuits of dynamic random access memories and static random access memories, programmable logic devices (PLDs), I/O circuits, and chip identification circuits. Conventional electrical fuses include a long, narrow fuse link connecting two larger plates defining an anode and a cathode. Electrical fuses may be dynamically programmed in real time by passing an electrical current through the fuse link.
A silicon-controlled rectifier (SCR) is a multiple-layer solid state device commonly utilized in current control applications. A silicon-controlled rectifier includes multiple electrodes or terminals and specifically includes an anode, a gate, and a cathode identifiable among its layers. In its high-impedance state, the silicon-controlled rectifier restricts current conduction to leakage current. However, a triggering signal applied to the gate can switch the silicon-controlled rectifier to a low-impedance state such that current is conducted between the anode and cathode. After the triggering signal is removed from the gate, the SCR remains in its low impedance state so long as the conducted current exceeds a holding current. When the conducted current drops below the holding current, the silicon-controlled rectifier returns to its high-impedance state.
Improved circuits for programming an electrical fuse, methods for programming an electrical fuse, and methods for designing a silicon-controlled rectifier for use in programming an electrical fuse are needed.